Synthesis and Reactivity of Cobalt(I) and Iridium(I) Complexes Bearing a Pentadentate <i>N</i>-Homoallyl-Substituted Bis(NHC) Pincer Ligand

Abstract

Two methods for the synthesis of the bis(imidazolin-2-ylidene)carbazolide cobalt(I) complex [Co(bimcaHomo)] (2) have been developed. The first route relies on the direct transmetalation of the in situ generated lithium complex [Li(bimcaHomo)] with CoCl(PPh3)3. The second route is a two-step synthesis that consists of the transmetalation of [Li(bimcaHomo)] with CoCl2 followed by reduction of the Co(II) complex to yield the desired Co(I) complex 2. The analogous iridium complex [Ir(bimcaHomo)] (4) was prepared by transmetalation of [Li(bimcaHomo)] or [K(bimcaHomo)] with [Ir(μ-Cl)(COD)]2. The catalytic activity of complexes 2 and 4 in the epoxide isomerization was tested in the absence and presence of H2. When [M(bimcaHomo)] (M = Ir (4), Rh (3)) was exposed to 1 bar of H2 at 80 °C, single crystals formed whose X-ray structure analyses revealed the hydrogenation of the N-homoallyl moieties and formation of the dimeric hydrido complexes [Ir(bimcan-Bu)(H)2]2 (7) and [Rh(bimcan-Bu)(H)2]2 (8).